Thanks for the welcome.
Rocky Rhodes, there are definitely predators in Australia that could attack from the sky. Fortunately and unfortunately I live in a built up area where these predators do not like to hang out.
My only concerns are snakes. Many of the snakes we have around here would not attach a fully grown chicken however they would love a feast of eggs. We do get pythons that could eat a chicken. In fact, last summer (your winter) we had a 12 foot python curled up behind our shed...
So far so good with the roofless run. Not indication that the chickens are being harassed by flying predators. Many of my friends have had roofless runs for a while now with no issues. I suppose there are some advantages to living in a built up area.
Cheers
Westy